In this extremely enlightening paper, Diaz et al. (2015) analyzed data on daily deaths due to natural causes in the city of Madrid (Spain) over the period 2001-2009, calculating the impact of both extreme hot and cold temperatures on mortality using Poisson regression models for specific age groups. And what did they thereby learn?

The five Spanish researchers report that "the mean intensity of the heat waves (0.8°C) was half that of the cold waves (1.7°C)." However, they found that the effect of cold on mortality was five times greater than that of heat. And if that sounds a bit extreme, they further note that the recent study of Gasparrini et al. (2015) showed, on a global basis, that cold-induced mortality is fully twenty times higher than that induced by heat.

This being the case, one would hope that any future global warming experienced by the Earth would be more strongly expressed by daily minimum temperatures than by daily maximum temperatures. And, fortunately, this is what has been found to have been the case to date, as has been demonstrated by the studies of Karl et al. (1984, 1991), Easterling et al. (1997), Donat et al. (2013) and Gasparrini et al. (2015), to name but a few.